It is known that various cationic supravital dyes have the capability of selectively staining cancerous and precancerous cells of epithelial tissue, as well as cells that are abnormal due to dysplasia, hyperplasia, tumorigenesis and other active surface lesions. For example, such dyes are disclosed in U.S. Pat. No. 4,321,251 to Mashberg, U.S. Pat. No. 5,372,801 to Tucci, et al., U.S. Pat. No. 5,882,627 to Pomerantz, and to Bernal U.S. Pat. No. 6,649,144. Also, see Chenz, Chinese Journal of Stomatology (27:44–47)(1992) and Filurin, Stomatologiia (Russian) (72:44–47)(1993). Other dyes that are similarly useful include rhodamine, alcian blue, malachite green, phenosafranin, acriflavine, pyronine Y, toluylene blue, and brilliant green. “Non-dye” compounds that are similarly useful include peonidin, oxythiamine, tiemonium iodide, elliptinium acetate and furazolium chloride.
The mechanism of such selective staining has been shown to involve absorption or entry of the marking agent molecule into the mitochondria of the cancerous or precancerous epithelial cells. This selective staining of the mitochondria of cancerous tissue is apparently due to the higher electrical potential (negative charge on the inside of the membrane of cancerous mitochondrial cells as compared to normal cells.
Although the mitochondrial marking agent also temporarily stains nearby non-cancerous tissue, it is released much more quickly from the normal tissue than from the mitochondria of the cancerous tissue. Thus the diagnosis of cancer is based on the continued retention of the dye in the cancerous tissue after it is autogenously released from the normal tissue. Proper selection of the elapsed time between application of the dye and the diagnostic observation of the tissue, permits the diagnostician to detect and selectively delineate cancerous or precancerous tissue sites on normal epithelial surfaces. This procedure permits identification of cancerous and potential cancerous sites with a high degree of accuracy, i.e., with a very low incidence of false negatives. However, because of differences in the tissues between patients and other variables such as skill of the diagnostician, etc., this diagnostic technique may also yield false positive results.
While false positives are much preferred over false negative results, it would, nevertheless, be highly desirable to reduce the rate of false positives, to avoid or reduce the necessity for invasive confirmatory testing and to avoid unnecessarily upsetting the patient.
To attempt to reduce the rate of false positives, it has been proposed to repeat the procedure after approximately two weeks, which gives time for healing of non-cancerous lesions or wounds which apparently tend to accumulate and retain the dye longer than normal tissue, even though they are not cancerous or precancerous. Of course, this repetition does prevent a number of false positives. However, the potential still remains for false positive due to other causes.